1. Field of the Invention
This invention relates to a method for cooling materials of low elastic limit such as aluminum strips, copper strips, and iron strips heated for the annealing.
2. Description of the Prior Arts
In prior arts, in the case where a metal strip (The term "metal strip" as used herein indicates a thin and lengthy band-like metal plate continuously rolled by a rolling mill. The thickness of the metal strip is normally less than 3.5 mm, and the plate has various widths.) is subject to cooling after it has been heated for heat treatment, even if the metal strip whose temperature has already decreased to a level below a definite value is cooled at a large temperature gradient, large thermal stresses are not introduced to the strip. However, when the temperature of the strip is not yet decreased to a level as noted above, cooling of the strip at a large temperature gradient produces large thermal stresses in the metal strip as shown by the broken lines in FIG. 5. When such large stresses occur, the stresses overcome the antibuckling stress of the metal strip and consequently give rise to wrinkles, in the metal strip, parallel to the moving direction thereof as shown in FIG. 7, resulting in a defective metal strip.